The US supreme court has struck down a key part of a landmark civil rights-era law designed to protect minority voters.

The decision drastically limits the federal government's powers to block laws that discriminate against black, Hispanic and other minority voters.

President Barack Obama has vowed to push to restore the protections, but it was unclear whether Republicans, who control the House of Representatives, would provide the support needed to offset the court ruling.

"I am calling on Congress to pass legislation to ensure every American has equal access to the polls," Mr Obama said.

The justices ruled the law, which affected mostly southern states with a history of discriminatory practices, was based on outdated data that did not reflect progress in race relations

The decision came after recent election cycles in which some states tried to impose last-minute changes to voting rules.

Critics complained those changes were aimed at suppressing the votes of minorities, while backers said they were designed to stop voter fraud.

The Voting Rights Act, a centrepiece of the American civil rights movement in the 1960s, was meant to ensure access to the ballot box for minorities, traditional allies of Democrats, in states where such voting rights were considered at risk.

Senate judiciary committee chairman Patrick Leahy promised to move quickly to restore the law in the 100-seat, Democratic-led Senate, saying the courts had "struck down the core of the most successful piece of civil rights legislation in this nation's history".

He said his panel would hold hearings in July and he would try to fashion a bipartisan bill, but it was unclear how far such a bill might advance.

Ballot box troubles discouraged voters

In recent elections, voters in some states have had to suffer through unusually long waits to cast their ballots and other ballot box problems which discouraged some from voting.

If any legislation emerges from Congress, it could try to tackle such problems.

Republicans, including House speaker John Boehner, were largely silent immediately after the court's ruling.

Senator John Cornyn of Texas, the second-ranking Republican in the Senate, suggested his state had been treated unfairly since it was among those that had to receive preclearance.

He complained that attorney-general Eric Holder had refused to approve voter identification laws in Texas and South Carolina.

The current version of the law was enacted with overwhelming bipartisan support in Congress in 2006 and signed by Republican president George W Bush.

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